1. Field of the Invention
The present invention is generally concerned with eyeglass frames and is more particularly directed to the front assembly, that is to say the part comprising two rim members or surrounds each adapted to hold a lens and joined to the other by a central bridge member and to the sides of which are hinged supporting side members.
To be more specific, the present invention is directed to the situation where the rim members or surrounds that a front assembly of this kind comprises are made wholly from a relatively rigid material, in practise from metal, to the exclusion of the case where they consist wholly or in part of a flexible tie member.
2. Description of the Prior Art
One of the problems to be overcome in manufacturing a front assembly in which the rim members or surrounds are made from a relatively rigid material results from the fact that in order to fit a lens into the rim members or surrounds it is necessary to provide a localized gap in their continuity so that they can be "opened out" and the fact that in order to "close" them after a lens has been fitted it is necessary, in order to retain the lens, to add to them closing means adapted to hold them in a closed configuration.
This is usually a screw.
In spite of the care taken in implementing a screw of this kind, and in spite of arrangements that may be adopted to prevent it unscrewing, it may nevertheless become unscrewed, prejudicing the retention of the lens concerned.
To avoid the disadvantages inherent to the use of a screw and those inherent to the use of any other closing means, it has already been proposed to use a shape memory material, to be more precise a shape memory alloy, in the construction of an eyeglass frame front assembly.
As is known, a shape memory alloy is an alloy which, as a result of temperature changes only, can change reversibly between two separate phases in the solid phase, the so-called austenitic phase and the so-called martensitic phase, for each of which it may be given a different shape that it spontaneously recovers at the corresponding temperature.
By virtue of such thermo-elastic behavior it is possible to obtain with a shape memory alloy a significant capacity for expansion between two specific temperatures, usually in the order of 5 to 8%, and in any event considerably greater than the usual capacity for thermal expansion.
In the international patent application filed under application No. PCT/US 84/02004 and published under the number WO85/02688, the thermo-elastic properties of shape memory alloys are used in the manufacture of eyeglass frame front assemblies.
In this international patent application, however, the rim members or surrounds of a front assembly of this kind are made from shape memory alloy over all of their circumferential length, even where the rim member or surround is reduced to two separate sections, one on the nose side and the other on the temple side, and these rim members or surrounds have, for the purpose of retaining the lens, a C-shaped transverse profile so as to grip the two opposite sides of a lens.
The corresponding implementations are inevitably costly and as they differ from conventional implementations using a bezel, for dealing with which practitioners have specific equipment, commercial use of them on a more widespread scale is difficult.
A general objective of the present invention is an arrangement which, while exploiting the benefits of shape memory alloys, is able to avoid these disadvantages and confer other advantages.